Android开发笔记之:Dialog的使用详解

dialog是任何系统都必须有的一个控件，作为辅助窗口，用于显示一些消息，或请求用户采取一引起操作等。
在android中也不例外，基本使用可能参看文档。
使用时的注意事项
1. back键能取消掉对话框(dismiss)，但是却不会触发其onokey和oncancel回调接口，所以如果你的对话框会改某些状态，一定要注意还有第三种方式取消对话框。
2. 尽量少用模态对话框(model dialog)，如果dialog.setcancellable(false)，就变成了一个模态对话框，除了程序内部把其dismiss，否则按什么键都无法将其取消。这是极差的用户体验，对话框本身就是一种干扰，再无法取消会把用户搞疯的。所以除非特别有必要，也即当执行某个操作时不希望被打破，才可以使用模态对话框。
3. 尽量少用对话框，它对用户是一种干扰，除非需要用户做操作，或者做出选择。通常的一般性的通知用toast或者notification就足够了。
4. 不要使用对话框风格的activity，也即把activity变成一个对话框。因为这样是自已定义的布局，与系统dialog的风格可能会不一致。最严重的是当系统风格发生变化，dialog的子类会变化，但activity式的对话框就不会变化。可以在ics中找一找activity对话框，你会发现其ok是在左边，而ics中系统dialog的ok都是在右边的。
5. 尽量保证dialog对象活在activity的生命周期之内，也即至多是在oncreate()和ondestroy()之间。
6. 要想到和测试到activity在其dialog.dismiss()之前死掉的情况。因为activity必须依附于某个正在显示的activity实例，当显示和取消的时候其activity实例必须存在，否则就会有"illegalargumentexception: view not attached to window manager"。

05-15 02:45:26.320: e/androidruntime(1161): java.lang.illegalargumentexception: view not attached to window manager
05-15 02:45:26.320: e/androidruntime(1161):     at android.view.windowmanagerimpl.findviewlocked(windowmanagerimpl.java:355)
05-15 02:45:26.320: e/androidruntime(1161):     at android.view.windowmanagerimpl.removeview(windowmanagerimpl.java:200)
05-15 02:45:26.320: e/androidruntime(1161):     at android.view.window$localwindowmanager.removeview(window.java:432)
05-15 02:45:26.320: e/androidruntime(1161):     at android.app.dialog.dismissdialog(dialog.java:278)
05-15 02:45:26.320: e/androidruntime(1161):     at android.app.dialog.access$000(dialog.java:71)
05-15 02:45:26.320: e/androidruntime(1161):     at android.app.dialog$1.run(dialog.java:111)
05-15 02:45:26.320: e/androidruntime(1161):     at android.app.dialog.dismiss(dialog.java:268)
05-15 02:45:26.320: e/androidruntime(1161):     at com.hilton.effectiveandroid.app.dialogdemo$1.handlemessage(dialogdemo.java:26)
05-15 02:45:26.320: e/androidruntime(1161):     at android.os.handler.dispatchmessage(handler.java:99)

7. dialog.show()必须在主线程里调用，但dialog.dismiss()却可以在任何线程中调用。
三种使用方式比较
1. 直接创建一个局部的dialog对象
优点是变量是局部的容易理解和维护。缺点是dialog对象难以控制，容易引发runtimeexception。
2. 把dialog对象变成activity的域
优点是dialog对象可以重复利用，且activity可以控制以保证dialog不会在activity生命周期外显示。是推荐的使用方式。
3. 用activity的方法oncreatedialog(), showdialog()和dismissdialog()
优点是frameworks会帮忙照看dialog，在大多数情况下这是推荐的做法。但是对于activity提前死掉的情况，此方法必有runtimeexception，且无法回避。
实例

public class dialogdemo extends activity {
    private static final int dismiss_dialog = 1;

    private progressdialog mbetterdialog;
    private handler mmainhandler = new handler() {
 @override
 public void handlemessage(message msg) {
     switch (msg.what) {
     case dismiss_dialog:
  dialog dialog = (dialog) msg.obj;
  dialog.dismiss();
  break;
     default:
  break;
     }
 }
    };
    @override
    protected void oncreate(bundle savedinstancestate) {
 super.oncreate(savedinstancestate);
 setcontentview(r.layout.dialog_demo);

 final button sucking = (button) findviewbyid(r.id.sucking);
 sucking.setonclicklistener(new view.onclicklistener() {
     public void onclick(view v) {
  final activity activity = dialogdemo.this;
  final progressdialog dialog = new progressdialog(activity);
  dialog.settitle("worst dialogging");
  dialog.setmessage("this is the worst dialogging scheme, never use it. this dialog is easy to " +
   "run out of its attached activity, yielding windowmanager#badtokenexception if the activity is gone when dismissing");
  dialog.setindeterminate(true);
  dialog.setcancelable(true);
  // you must do the show in main thread anyway
  dialog.show();
  new thread(new runnable() {
      public void run() {
   systemclock.sleep(10000);
   /*
    * illegalargumentexception: view not attached to window manager
    * if the activity showing the dialog was killed before dismiss() out of rotation or locale changed,
    * the dialog will gone with activity, but when dismiss() yields "illegalargumentexception: view not attached to
    * window manager".
    * checking isshowing() won't help.
    * checking activity.isfinishing() won't help, either.
    * dismiss it in main thread also won't give any help.
    */
   // this won't work
//   if (dialog.isshowing()) {
//       dialog.dismiss();
//   }
//   if (!activity.isfinishing()) {
//       dialog.dismiss();
//   }
   message msg = message.obtain();
   msg.what = dismiss_dialog;
   msg.obj = dialog;
   mmainhandler.sendmessage(msg);
      }
  }).start();
     }
 });

 final button better = (button) findviewbyid(r.id.better);
 better.setonclicklistener(new view.onclicklistener() {
     public void onclick(view v) {
  mbetterdialog = new progressdialog(dialogdemo.this);
  mbetterdialog.settitle("better dialogging");
  mbetterdialog.setmessage("this dialogging can be used. the dialog object is a field of its activity, so activity can" +
    " control it to make sure dialog only lives within activity lifecircle");
  mbetterdialog.setindeterminate(true);
  mbetterdialog.setcancelable(true);
  // you must do the show in main thread anyway
  mbetterdialog.show();
  new thread(new runnable() {
      public void run() {
   systemclock.sleep(10000);
   /*
    * this is much better, mbetterdialog is a field of its activity, so activity can take care of it in order
    * to make sure dialog only live within activity's life circle, to avoid any unexpected exceptions.
    */
   // this really works
       if (mbetterdialog != null && mbetterdialog.isshowing()) {
           mbetterdialog.dismiss();
       }
      }
  }).start();
     }
 });

 final button optional = (button) findviewbyid(r.id.optional);
 optional.setonclicklistener(new view.onclicklistener() {
     @suppresswarnings("deprecation")
     public void onclick(view v) {
  showdialog(0);
  new thread(new runnable() {
      public void run() {
   systemclock.sleep(10000);
   /*
    * this way works best for most of time, except if activity died before dismissing, exception must be
    * thrown: "illegalargumentexception: view not attached to window manager".
    * although activity takes care of its belonging dialog, there is no way to operate it manually any more.
    * first you do not have reference to dialog object and second, any manual operation only interferences
    * and breaks state maintained by frameworks.
    */
   dismissdialog(0);
      }
  }).start();
     }
 });
    }
    @override
    protected dialog oncreatedialog(int id) {
 progressdialog d = new progressdialog(this);
 d.settitle("optional dialogging");
 d.setmessage("this dialogging scheme works best for most times, the dialogs are all taken care of by activitys and frameworks" +
   ". except for activity being killed during dialog showing");
 d.setindeterminate(true);
 d.setcancelable(true);
 return d;
    }
    @override
    protected void ondestroy() {
 super.ondestroy();
 // activity is dying, all its belonging dialogs should be dismissed, of course.
 if (mbetterdialog != null && mbetterdialog.isshowing()) {
     mbetterdialog.dismiss();
     mbetterdialog = null;
 }
 // for dialogs showed via showdialog(int), no way to stop it in ondestroy()
// dismissdialog(0); // cause "illegalargumentexception: no dialog with id 0 was ever shown via activity#showdialog"
       // this is because activity has to manage its dialog during onpause() and onresume() to restore
                   // dialogs' state. so if you manually dismiss it in ondestroy(), it will cause je.

// removedialog(0);// cause "illegalargumentexception: no dialog with id 0 was ever shown via activity#showdialog", when
   // dismissing in thread.
               // this is because activity has to manage its dialog during onpause() and onresume() to restore
                     // dialogs' state. so if you manually dismiss it in ondestroy(), it will cause je.
    }
}